Apparatus and method of manufacture for integrated circuit and CMOS device including epitaxially grown dielectric on silicon carbide

ABSTRACT

An integrated circuit, or portion thereof, such as a CMOS device, includes an epitaxially grown dielectric on a silicon carbide base. The epitaxially grown dielectric forms a gate dielectric and the silicon carbide base serves as a channel region for the CMOS device. In various embodiments, the epitaxially grown dielectric may be a crystalline carbon or carbon-containing film.

FIELD OF THE INVENTION

This invention relates to semiconductor integrated circuits (ICs). Inparticular, this invention relates to new and improved techniques forforming a CMOS device, such as a MOSFET, within the IC.

BACKGROUND OF THE INVENTION

A significant trend throughout IC development has been to reduce thesize of the components of the IC's. As the size is reduced, theperformance requirements of the materials of the components become morestringent. For CMOS devices (e.g. CMOS transistors) in particular,increased performance requirements have generally been met byaggressively scaling the thickness of the gate dielectric and the lengthof the channel of the transistors. As continued attempts have been madeto scale down CMOS technology, however, the performance requirements forthe CMOS devices have proven so stringent that scaling of either thegate dielectric and/or the channel length has become a very difficultand/or impractical solution for meeting the high performancerequirements.

A gate dielectric thickness of about ten Angstroms and smaller isanticipated in next generation CMOS devices. Such thin gate dielectricsface high gate leakage current, which is detrimental to deviceperformance and overall power consumption.

It has been suggested to use dielectric materials having a dielectricconstant (K) in a range of about 7 to 30 as the gate dielectric for CMOSdevices. Such a range for K is considerably larger than that for silicondioxide (K=3.9), which is commonly used as the gate dielectric. Suchhigher-K dielectric materials have the potential to reduce gate leakagecurrent and thus enable much thinner gate dielectric layers for thesmaller dimensions required for new CMOS devices.

However, the higher-K dielectric materials have several limitations thathave made it difficult to incorporate these materials into CMOS devices.For instance, the processes for forming the higher-K dielectricmaterials are generally not compatible with conventional CMOSfabrication processes. Therefore, incorporation of such materials intoCMOS devices can require significant changes to the CMOS fabricationprocesses, which can significantly affect the cost of the resulting CMOSdevices.

Additionally, the higher-K dielectric materials do not form a goodinterface with the silicon-based materials onto which the dielectricmaterial must be deposited. Problems thus arise at the interface betweenthe higher-K dielectric material and the substrate and gate electrode.For example, high interface traps may be created between the materiallayers (especially between the gate dielectric and the substrate). Also,channel carrier mobility may be degraded by the higher-K dielectricmaterials. Additionally, the higher-K dielectric materials have problemswith fixed dielectric charges and thermal stability. Furthermore, thepresence of the higher-K dielectric materials may limit the temperatureat which further processing may be performed.

To meet the increased performance requirements of the smaller CMOSdevices, it has also been suggested to increase the mobility of thecarriers in the channel region. For example, strained-Silicon(“strained-Si” or “SSI”) may be incorporated into the channel region,since strained-Si is known to have greater carrier mobilitycharacteristics than does the silicon that has been more commonly usedin the channel region of CMOS devices. (K. Rim, S. Koester, M. Hargrove,J. Chu, P. M. Mooney, J. Ott, T. Kanarsky, P. Ronsheim, M. Ieong, A.Grill, and H.-S. P. Wong, “Strained-Si NMOSFETs for High PerformanceCMOS Technology,” 2001 Symposium on VLSI Technology Digest of TechnicalPapers, 2001, p. 59.) Additionally, strained silicon carbide(“strained-SiC”) may be incorporated into the channel region, sincestrained-SiC also has greater carrier mobility characteristics. (AkiraYamada, Tatsuro Watahiki, Shuhei Yagi, Katsuya Abe, and Makoto Konagai,“Epitaxial Growth of Strained Si1-xCx on Si and Its Application toMOSFET,” International Symposium on Quantum Effect Electronics, 2002.)

Formation of a strained-Si layer on a semiconductor wafer has been donein a variety of ways. One technique involves complex fabricationprocesses, which includes multiple epitaxial growth steps. For example,a relatively thick, graded buffer silicon-germanium (SiGe) film 100 isepitaxially grown onto a silicon, or semiconductor, substrate 102,followed by epitaxial growth of a relaxed SiGe film 103 onto the bufferSiGe film 100 and epitaxial growth of a strained-Si layer 104 onto therelaxed SiGe film 103, as shown in FIG. 1. The strain in the strained-Silayer 104 is induced by the underlying SiGe films 100 and 103. Thebuffer SiGe film 100 is typically formed with a graded concentration ofGe in the Si, wherein the concentration of the Ge is slowly increased asthe buffer SiGe film 100 is grown on the substrate 102. In order toproduce high quality strained-Si it is essential to carefully controlthe stoichiometry of the layer during the SiGe epitaxial growth process.Thus, the introduction of the gases into the epitaxial growth reactorchamber (not shown) must be carefully varied during fabrication of thebuffer SiGe film 100. In this manner, the spacing between the atoms inthe crystalline structure of the buffer SiGe film 100 is slowlyincreased from the beginning 106 to the surface 108 of the buffer SiGefilm 100. When the relaxed SiGe film 103 and the Si layer 104 areepitaxially grown on top of the buffer SiGe film 100, the increasedspacing is effectively maintained between the Si atoms which leads to astraining of the Si layer 104.

A conventional CMOS device 110, having a conventional gate oxide region118 and conventional source, drain and gate electrodes 112, 114 and 116,is then fabricated on top of the strained-Si layer 104. The increasedspacing between the Si atoms in the strained-Si layer 104 enhances themobility of the carriers in the channel region, which is formed in thestrained-Si layer 104 under the gate oxide 118 and between the sourceand drain 112 and 114.

The presence of the strained-Si layer 104 sets limitations on thetemperatures at which any subsequent processing steps may be performed,thereby limiting the flexibility with which the subsequent processingsteps may be performed. Furthermore, the relatively thick SiGe film 100acts as a thermal insulation layer, so the CMOS devices formed thereonare susceptible to self-heating during operation of the IC, therebydegrading the performance capability of the IC. Also, isolation of theCMOS device 110, typically with shallow trench isolation, must bedefined in both the strained-Si layer 104 and the SiGe films 100 and 103as well as in the silicon substrate 102, which adds to the complexity ofthe overall IC fabrication. Furthermore, this technique is prone todefects, which may occur in the SiGe films 100 and 103 and, thus,propagate into the strained-Si layer 104 and higher layers of materials.Such defects may involve threading dislocations in the crystallinestructure of the various layers as well as “misfit” dislocations at theinterface between the relaxed SiGe film 103 and the strained-Si layer104. The dislocations, as well as precipitates nucleated at thedislocation core area, negatively impact carrier mobility, gate oxidequality and overall device performance.

The use of the strained-SiC film in the channel region of the CMOSdevice 110, as shown in FIG. 2, may be simpler than the strained-Sitechnique described above. An epitaxial growth process is performed togrow a crystalline SiC film 120 on the silicon substrate 102. Sincecarbon is a smaller atom than silicon, the presence of the carbon in theSiC film 120 induces a tensile strain in the crystalline lattice of theSiC film 120 due to the underlying silicon substrate 102, which enhancesthe mobility of the carriers therein. The CMOS transistor 110, havingthe source, drain and gate electrodes 112, 114 and 116 and the gateoxide region 118, is then fabricated on top of the strained-SiC layer120, with the gate oxide region 118 being deposited onto the epitaxiallygrown SiC film 120.

Neither of these carrier-mobility-improvement techniques compensates forthe problems that arise in the use of the suggested higher-K dielectricmaterials for the gate oxide region 118. In particular, the inferiorinterface between the gate oxide region 118 and adjacent layers remainsa significant issue for the CMOS processing. Special care must be takenin the formation of the gate oxide region 118 and in many subsequentprocesses. Additionally, the strained-Si layer 104 sets limitations onthe temperatures at which any subsequent processing steps may beperformed, thereby limiting the flexibility with which the subsequentprocessing steps may be performed. Therefore, the resulting over-allfabrication is quite complex, time-consuming and costly.

It is with respect to these and other considerations that the presentinvention has evolved.

SUMMARY OF THE INVENTION

The present invention evolved out of the discovery of materials that canbe used in channel and gate dielectric structures of next-generationCMOS devices and that have such bonding and interface characteristics asto avoid or overcome the interface problems of the higher-K dielectricmaterials discussed in the background. With a SiC base, which preferablyserves as a channel region of the overlying CMOS device, a compatiblegate dielectric material is epitaxially grown thereon to a desiredthickness depending on the EOT (equivalent oxide thickness) required forthe particular application.

In various embodiments, the gate dielectric material is preferablycarbon or a carbon-containing material, which has a mid-level dielectricconstant (K) of about 5.7 or a range greater than about 4.5,significantly greater than the K=3.9 for conventional silicon dioxide.Additionally, the carbon and carbon-containing materials are fullycompatible with the underlying SiC, so nucleation and growth of the gatedielectric material on the SiC base material is not an issue. Theresulting epitaxially grown gate dielectric material has a fullycrystalline structure. Thus, the interface between the gate dielectricand the underlying material is considerably better and any interfacecharge traps and fixed dielectric charges are considerably lower thanthose for the higher-K dielectric materials described in the backgroundas suggested for use with next-generation CMOS devices.

Additionally, in a particular embodiment, the SiC base is preferably aSiC film epitaxially grown on a silicon substrate of a semiconductorwafer. In another particular embodiment, the SiC base is preferably partof a SiC substrate on which the IC fabrication is performed.

Furthermore, in another particular embodiment, a gate electrode materialof SiC is preferably epitaxially grown or deposited on the carbon orcarbon-containing gate dielectric material. In this manner, a goodinterface is also achieved between the gate electrode and the gatedielectric. Thus, the gate dielectric has a good interface on both thebottom and the top thereof.

A more complete appreciation of the present invention and its scope, andthe manner in which it achieves the above noted improvements, can beobtained by reference to the following detailed description of presentlypreferred embodiments of the invention taken in connection with theaccompanying drawings, which are briefly summarized below, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, broken, cross-sectional view of a portion of aprior art integrated circuit.

FIG. 2 is a simplified, broken, cross-sectional view of a portion ofanother prior art integrated circuit.

FIG. 3 is a simplified, broken, cross-sectional view of a portion of anintegrated circuit in which the present invention is incorporated andwhich has been fabricated according to the present invention.

FIG. 4 is a simplified, broken, cross-sectional view of a portion ofanother integrated circuit in which an alternative embodiment of thepresent invention is incorporated and which has been fabricatedaccording to the alternative embodiment of the present invention.

DETAILED DESCRIPTION

A portion of an integrated circuit (IC) 200 which incorporates a firstembodiment of the present invention and which is formed by themethodology of the first embodiment of the present invention is shown inFIG. 3. The IC 200 includes a strained-SiC layer, or film, 202 (or itsderivatives, such as SiGeC) formed by SiC epitaxial growth above asemiconductor layer 204, such as a silicon substrate. The strained-SiClayer 202 serves as a base for a CMOS device 206, such as an N or PMOSFET. The CMOS device 206 generally includes a gate dielectric region210, a gate electrode region 208, source and drain regions 212 and 214,a channel region 216 and gate electrode spacers 218. The channel region216 is within the strained-SiC layer 202 between the source and drainregions 212 and 214 under the gate dielectric region 210. The source anddrain regions 212 and 214 include doped regions 220 and 222 on oppositesides of the gate electrode region 208 under the gate electrode spacers218.

The gate dielectric region 210 is epitaxially grown on the strained-SiClayer 202, as opposed to being deposited thereon as described in thebackground. Thus, the gate dielectric region 210 is selected to be fullycompatible with the strained-SiC layer 202 and has a fully crystallinestructure. Due to the fully crystalline structure and compatibility, thegate dielectric region 210 provides an effective dielectric functionwith a mid-level dielectric constant K (e.g. about 5.7 or in a rangegreater than about 4.5) superior to the dielectric capabilities of themid-to-high-K (e.g. K=7-30) dielectric materials described in thebackground. Additionally, the interface charge traps and fixeddielectric charge problems, among other issues, make the mid-to-high-Kdielectric materials inferior to the epitaxially grown gate dielectricregion 210, since these problems are significantly reduced under thepresent invention. Thus, the crystalline gate dielectric region 210,particularly in combination with the strained-SiC layer 202, enables ahigh-performance device primarily due to a reduced gate dielectric EOT(and an enhanced channel mobility), while avoiding other deterioratingfactors attributed to devices with the higher-K dielectrics and thestrained-Si channel as described in the background.

Since the gate dielectric region 210 is epitaxially grown, there is ahigh level of controllability over the thickness of the gate dielectricregion 210. The background dielectric materials do not allow this levelof controllability over thickness because these materials are deposited,rather than grown.

In various embodiments, the gate dielectric region 210 is a crystallinecarbon or carbon-containing derivative (e.g. carbon derivate variationsmay contain silicon or fluorine). Carbon and its derivatives arecompatible with SiC such that these materials can be epitaxially grownon the strained-SiC layer 202. Other materials may also be compatiblewith SiC and may be epitaxially grown on the strained-SiC layer 202 toform the gate dielectric region 210.

In a particular embodiment, the gate electrode region 208 is epitaxiallygrown on the gate dielectric region 210. In this manner, compatibilityand a good interface between the gate electrode region 208 and the gatedielectric region 210 is ensured. Thus, interface problems both aboveand below the gate dielectric region 210 are minimized or eliminated,and performance of the CMOS device 206 is enhanced. In a preferredvariation of this particular embodiment, the gate electrode region 208is epitaxially grown SiC. Alternatively, in another embodiment, the gateelectrode region 208 is a deposited SiC film. In yet another embodiment,the gate electrode region 208 is a deposited polysilicon film. Each ofthese embodiments, among others, enables different interfacecharacteristics or quality. The exact material and formation techniquefor the gate electrode region 208 will depend on the requirements of theparticular application or situation.

An advantage of the present invention is that the portion shown of theIC 200 is fully compatible with conventional CMOS processing techniques.The procedure for fabricating the portion shown of the IC 200 may beperformed in a variety of ways. An exemplary fabrication procedure mayinclude the epitaxial growth of the strained-SiC layer 202 on thesemiconductor layer 204. Similarly, formation of the gate dielectricregion 210 may include the epitaxial growth of a crystalline film (e.g.the crystalline carbon or carbon-containing materials) on thestrained-SiC layer 202 followed by patterning and etching of thecrystalline film to leave the desired gate dielectric region 210. Sincethe preferred gate dielectric materials (e.g. the carbon andcarbon-containing materials) are fully compatible with the underlyingSiC, nucleation and growth of the gate dielectric region 210 on thestrained-SiC layer 204 is not an issue. The resulting epitaxially growngate dielectric region 210 has a fully crystalline structure. Due to thecompatibility of the materials and the fully crystalline structure ofthe gate dielectric region 210, the interface between the gatedielectric region 210 and the underlying strained-SiC layer 202 isconsiderably better and any interface charge traps and fixed dielectriccharges are considerably lower than those for the higher-K dielectricmaterials described in the background as suggested for use withnext-generation CMOS devices.

The doping of the doped regions 220 and 222 may be performed at anappropriate point within this procedure. Formation of the gate electroderegion 208 and the gate isolation regions 218 are performed in anyappropriate order, such as placement of a conductive or semiconductivefilm (e.g. epitaxial growth or deposition of a SiC film or deposition ofa polysilicon film) for the gate electrode region 208 over the gatedielectric region 210 and the strained-SiC layer 202 followed bypatterning and etching of the conductive film followed by deposition,patterning and etching of a dielectric film for the gate isolationregions 218.

A portion of an integrated circuit (IC) 300 which incorporates a secondembodiment of the present invention and which is formed by themethodology of the second embodiment of the present invention is shownin FIG. 4. The IC 300 includes a SiC substrate 302, instead of a siliconsubstrate. The SiC substrate 302 serves as the base for a CMOS device306, similar to the CMOS device 206 (FIG. 3). The CMOS device 306generally includes a gate electrode region 308, a gate dielectric region310, source and drain regions 312 and 314, a channel region 316 and gateisolation regions 318. The channel region 316 is within the SiCsubstrate 302 between the source and drain regions 312 and 314 under thegate dielectric region 310. The source and drain regions 312 and 314include doped regions 320 and 322 on opposite sides of the gatedielectric region 310 under the gate isolation regions 318 within theSiC substrate 302.

The use of the SiC substrate 302 eliminates the need to epitaxially growthe strained-SiC layer 202 (FIG. 3) on the semiconductor layer 204 (FIG.3). Therefore, fabrication of the IC 300, at least of the portion shownin FIG. 4, is simplified over the embodiment shown in FIG. 3. Wafers ofthe SiC substrate 302, however, may be more expensive than wafers of aSi substrate (e.g. semiconductor layer 204, FIG. 3). Selection betweenthe SiC and Si wafers may depend on the availability of the SiC wafersand the requirements of the particular application.

The gate dielectric region 310 may be formed similar to the gatedielectric region 210 (FIG. 3). Thus, the gate dielectric region 310 ispreferably an epitaxially grown crystalline dielectric material, such ascarbon or carbon-containing materials. Likewise, with slight variations,the remaining parts of the CMOS device 306 may be formed similar tocorresponding parts of the CMOS device 206 (FIG. 3). The doping of thedoped regions 320 and 322 may be somewhat different from the doping ofthe doped regions 220 and 222 (FIG. 3) since the materials into whichthe dopants (not shown) are placed are slightly different in each case(e.g. the strained-SiC layer 202 and the semiconductor layer 204 for thedoped regions 220 and 222, and the SiC substrate 302 for the dopedregions 320 and 322).

Presently preferred embodiments of the present invention and many of itsimprovements have been described with a degree of particularity. Thisdescription is of preferred examples of implementing the invention, andis not necessarily intended to limit the scope of the invention. Thescope of the invention is defined by the following claims.

1. An integrated circuit comprising: a silicon carbide base; adielectric film epitaxially grown on the silicon carbide base, theepitaxially grown dielectric film including crystalline carbon; and aCMOS device including a channel region formed in the silicon carbidebase and a gate dielectric formed by the epitaxially grown dielectricfilm.
 2. An integrated circuit as defined in claim 1 wherein: theepitaxially grown dielectric film has a dielectric constant larger than4.5.
 3. An integrated circuit as defined in claim 1 further comprising:a silicon substrate; wherein the silicon carbide base is formed on thesilicon substrate.
 4. An integrated circuit as defined in claim 1wherein: the silicon carbide base comprises a silicon carbide substrate.5. An integrated circuit as defined in claim 1 further comprising: asilicon carbide region formed on the epitaxially grown dielectric film;wherein the CMOS device further includes a gate electrode formed by thesilicon carbide region.
 6. An integrated circuit as defined in claim 3wherein: the silicon carbide base is epitaxially grown on the siliconsubstrate.
 7. An integrated circuit as defined in claim 6 wherein: theepitaxially grown silicon carbide base is a strained silicon carbidefilm.
 8. An integrated circuit as defined in claim 5 wherein: thesilicon carbide region is epitaxially grown on the epitaxially growndielectric film.
 9. An integrated circuit as defined in claim 5 wherein:the silicon carbide region is deposited on the epitaxially growndielectric film.